In conventional magnetic gradiometer survey applications that localize magnetic anomalies or targets, a fixed-baseline magnetic gradiometer is typically used. In general, such gradiometers include two or more scalar magnetometers held by a rigid frame to maintain known relative positions. For example, the magnetometers can be mounted/fixed on a moving platform when used to search a particular region. In this typical case, the distance between the individual magnetometers, known as the baseline, has a fixed value that depends on multiple factors including the desired overall size of the gradiometer, the constraints imposed by the platform geometry, the magnetometer technology (e.g., footprint of each element, power requirements, cross-talk considerations, ruggedization aspects, etc.), and the expected magnetic moment of the targets of interest. Existing state-of-the-art magnetic gradiometers cannot be easily modified in the field to allow for variation of their baseline length or orientation in three-dimensional space.
The limitations and disadvantages associated with the above-described conventional magnetic gradiometer sensing systems and methods include the following:
The fixed baseline limits the range of targets the gradiometer can measure. In survey applications, long baselines are desirable for localizing high magnetic moment targets, while short baselines are needed for low magnetic moment targets.
In a conventional long baseline gradiometer, the device can become very large leading to an impractical device/platform whose size/weight requirements limit the number of possible platforms and increase storage space requirements.
Three or more total field (scalar) magnetometers are required in a fixed gradiometer to obtain unambiguous localization of a magnetic object using data from a single pass near the object.